Ensuring the quality and appropriate state of sleep is essential for maintaining one's health. It is necessary to understand a sleep state, including an amount of sleep time from when a person goes to bed to when the person wakes, the depth of the sleep, and so on, in order to evaluate the sleep state. The devices disclosed in Patent Literature 1-3 have been proposed as devices for understanding such a sleep state.
Patent Literature 1 discloses a device that determines a subject is in bed when the subject's heart rate, measured based on a signal detected from a sensor, exceeds an in-bed determination threshold, and in the case where, in segments in which it has been determined that the subject is in bed, a degree of variation in the signal level in a plurality of stable segments (segments where the signal level does not vary greatly) is low, determines that a heart rate distribution in the segments for which the determination has been made is due to external noise rather than biological factors.
Patent Literature 2 and Patent Literature 3 disclose devices that determine a sleep state of a measurement subject using a vibration sensor that detects vibrations in a location where the measurement subject is sleeping.